Water Content Of Clouds

Have you ever wondered how much water is in clouds? This image is a global map of "cloud water content"--a measure of how many grams of water per square meter you would get if you drained all the water out of the clouds into a flat layer on the ground. White areas show clouds with as much as 1,000 grams of water per square meter; pink shades show areas with about 500 grams of water per square meter, and purple shows areas with little or no cloud water content.

Using the MODIS, flying aboard NASA's Terra and Aqua satellites, scientists can measure how much visible and near-infrared light is reflected by clouds back up into space. The more particles contained within a cloud, the more it reflects visible light. And the larger the cloud particle size, the more it absorbs near-infrared light. Thus, by measuring how much light a cloud prevents from traveling down through a column of atmosphere (or cloud optical thickness) and the size of the particles that make up the cloud, scientists can estimate how much water is in the cloud.

In short, the soggier the cloud, the more it reflects sunlight back to space and the more it cools Earth's surface. Cloud water content and cloud particle size are also important for global studies of precipitation. Smaller cloud particles tend to remain suspended in the atmosphere longer, and so clouds comprised of smaller particles tend to linger longer and exert a greater cooling influence on the surface.

This data shows the earth between May 1 and June 1, 2007.